There is generally known a sheet processing device connected to an image forming apparatus. The sheet processing device is called, for example, a post-processing device. The sheet processing device includes, for example, a punching device. The punching device performs a punching process on a sheet member conveyed from the image forming apparatus.
In addition, there is known that, in the punching device, a plurality of punching portions and a sensor are supported on a support member that can be displaced in the width direction of the sheet member, and the plurality of punching portions perform the punching simultaneously at a plurality of spots on the sheet member. In this case, the sensor detects an end of the sheet member in the width direction of the sheet member. Furthermore, the support member is positioned based on a position at a point in time when an end of the sheet member was detected by the sensor. In this state, the plurality of punching portions operate simultaneously (see, for example, PTL 1).